The present invention relates to a semiconductor radiation detector that is capable of high energy resolution with a semiconductor detection device such as silicon or germanium which can be cooled to a temperature in the neighborhood of the temperature of liquid nitrogen with a refrigerator that makes use of the adiabatic expansion of air or nitrogen gas (said refrigerator is hereinafter referred to as an adiabatic expansion effect refrigerator).
Semiconductor radiation detectors that are capable of high energy resolution with a semiconductor detection device such as silicon or germanium have heretofore been used in qualitative and quantitative analyses of X-rays or gamma-rays. As shown in FIG. 1, the semiconductor radiation detection device 3 is conventionally cooled with liquid nitrogen 2 in a cooling vessel 1. One problem with this system is that the need to handle liquid nitrogen renders the operation and maintenance of the detector quite time-consuming and cumbersome. In addition, because of the limits on the efforts to reduce the size of the cooling vessel, much difficulty is involved in making the detector compact; for instance, when the detector is completely shielded so as to enable its use in a strong radioactive field, the overall size of the detection equipment including the shield is inevitably increased.
FIG. 2 shows a system of radiation ray detector that has been proposed to enable its cooling in the absence of liquid nitrogen and which features a potential for size reduction. This system is designed to cool the semiconductor detection device 9 with a refrigerator 6 that makes use of the adiabatic expansion of gases. As shown, the pressure of air or nitrogen supplied from a cylinder 14 is lowered with a reducing valve unit 13 and, after being passed through a filter 11 to have any impurities removed, the gas is permitted to flow through an adiabatic expansion effect refrigerator 6 so as to cool the detection device 9. The refrigerator used in this system can be made sufficiently smaller in size to render the overall detector system compact.
However, if the flow rate of gas supplied to the detector system shown in FIG. 2 is increased, the gas being released through the adiabatic expansion valve 7 causes an increased amount of air vibration in the cooling section and this will reduce the energy resolution of the detector.